The present invention relates in general to a sheet metal forming die assembly. More specifically, but without restriction to the particular embodiment and/or use which is shown or described for purposes of illustration, the present invention relates to an improved sheet metal draw forming die assembly with textured surfaces.
Sheet metal draw forming and stamping die assemblies have been used for many years to form various sheet metal components. Draw forming press assemblies are used in the automotive industry to form various outer body panels such as a hood, roof or door exterior panel. A typical configuration for an outer body panel draw forming press assembly would include a press, an upper die, a lower punch, a lower binder, a lower shoe, a press bed and cushion pins.
As is well known in the art, draw beads and lock beads are commonly used in the upper die and lower binder mating surfaces to control the flow of the sheet metal during the forming process. The mating components of the draw and lock beads are machined into the binder and upper die mating surfaces, respectively. Draw and lock beads usually consist of geometric shapes that include sharp radii and are designed to locally control and even stop sheet metal flow during the forming operation. A disadvantage of the draw and lock beads is that they are subject to high wear. To service and repair the beads, the die and binder are typically removed from the press.
Utilizing draw and/or lock beads in the press assemblies can require additional press tonnage to prevent uplift between the binder and upper die as the sheet metal attempts to flow around the bead geometry during the draw forming process. Furthermore, additional material is required beyond the product trim line to form the sheet metal into the bead configuration. In addition, draw and lock beads can cause sheet metal wrinkling and stringers as the sheet metal flows in relation to the beads during the draw forming process. The die and binder repairs, sheet metal stringers and wrinkles, additional press tonnage and extra sheet metal stock required for the bead geometry all increase the costs and decrease the productivity of manufacturing automotive sheet metal outer body panels.
Thus, there is a need for improved sheet metal flow control in a draw forming die assembly that overcomes the aforementioned drawbacks incurred when using draw and/or lock beads to control the sheet metal flow during the forming process.
Accordingly, the present invention eliminates or significantly reduces the need for draw and/or lock beads by providing a textured die surface for controlling sheet metal flow during the draw forming process. In accordance with one aspect of the present invention, a textured die surface is formed on a binder surface of a draw forming die assembly that is arranged to engage the sheet metal. The textured die surface increases the coefficient of friction between the binder surface and the sheet metal when the sheet metal is clamped between the binder surface and an upper die assembly perimeter surface during the draw forming process.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.